1. Field of the Invention
The present invention relates generally to circuit interrupters and, more particularly, to a fastener that can be employed in a circuit breaker application, the fastener being lockable to resist release thereof. The invention also relates to a circuit breaker employing a lockable fastener.
2. Background Information
Circuit interrupters, such as circuit breakers, are employed in diverse capacities in power distribution systems. A circuit breaker includes, for example, a line conductor, a load conductor, a fixed contact and a movable contact, with the movable contact being movable into and out of electrically conductive engagement with the fixed contact to switch the circuit breaker between an on or closed position and an off or open position, or between the on or closed position and a tripped position. The fixed contact is electrically conductively engaged with one of the line and load conductors, and the movable contact is electrically conductively engaged with the other of the line and load conductors.
The movable contact is typically disposed on a movable contact arm. In some circuit breakers, the movable arm may be disposed upon a structure within the interior of the circuit breaker and a flexible shunt is employed to electrically conductively connect the movable arm with its associated conductor. In other circuit breakers, it may be desirable to pivotably mount the movable arm directly on the associated conductor. In such a circumstance, a fastener may be employed in making the pivotable connection between the movable arm and the conductor. The fastener must provide sufficient contact forces between the conductor and the movable arm to provide electrically conductive engagement therebetween; however, the contact forces cannot be so great as to cause so much friction between the movable arm and the conductor that the pivoting action of the arm is impaired. It, thus, has been known to provide a threaded fastener for fastening a movable contact arm to a conductor, with the threaded fastener being tightened to a highly specific level of torque that achieves an agreeable balance between electrical conductivity and friction.
Such devices have not, however, been without limitation. It is understood that repeated opening and closing of the contacts, whereby the movable arm pivots between a closed position and an open position, can result in gradual loosening of the threaded fastener that pivotably mounts the movable arm to the conductor. Such loosening changes the torque of the fastener and, thus, the conductive/frictional characteristics of the pivotable connection between the movable arm and the conductor, which is undesirable.
It is also known that space is extremely limited within the confines of a circuit breaker. As such, any solution to the fastening problem must occupy a minimum of space.
It is, thus, desired to provide an improved fastener that is reliably lockable and that occupies a minimum of space.
Accordingly, there is room for improvement in lockable fasteners and in circuit breakers employing lockable fasteners.